[FIX] mail: visitor to portal_user should keep livechat channel

adapting #20279 to v10

Before this commit, when starting a livechat session as a public user and continuing as a portal user, the livechat crashed
(the poral user couldn't see the channel created before as Admin)

After this commit, the conversation is kept and security insured by the uuid in the cookie

OPW 775568

addons/mail/controllers/bus.py

@@ -36,18 +36,16 @@ def _poll(self, dbname, channels, last, options):
     # --------------------------
     @route('/mail/chat_post', type="json", auth="none")
     def mail_chat_post(self, uuid, message_content, **kwargs):
-        request_uid = self._default_request_uid()
         # find the author from the user session, which can be None
         author_id = False  # message_post accept 'False' author_id, but not 'None'
         if request.session.uid:
             author_id = request.env['res.users'].sudo().browse(request.session.uid).partner_id.id
         # post a message without adding followers to the channel. email_from=False avoid to get author from email data
-        mail_channel = request.env["mail.channel"].sudo(request_uid).search([('uuid', '=', uuid)], limit=1)
-        message = mail_channel.sudo(request_uid).with_context(mail_create_nosubscribe=True).message_post(author_id=author_id, email_from=False, body=message_content, message_type='comment', subtype='mail.mt_comment', content_subtype='plaintext', **kwargs)
+        mail_channel = request.env["mail.channel"].sudo().search([('uuid', '=', uuid)], limit=1)
+        message = mail_channel.sudo().with_context(mail_create_nosubscribe=True).message_post(author_id=author_id, email_from=False, body=message_content, message_type='comment', subtype='mail.mt_comment', content_subtype='plaintext')
         return message and message.id or False
 
     @route(['/mail/chat_history'], type="json", auth="none")
     def mail_chat_history(self, uuid, last_id=False, limit=20):
-        request_uid = self._default_request_uid()
-        channel = request.env["mail.channel"].sudo(request_uid).search([('uuid', '=', uuid)], limit=1)
-        return channel.sudo(request_uid).channel_fetch_message(last_id, limit)
+        channel = request.env["mail.channel"].sudo().search([('uuid', '=', uuid)], limit=1)
+        return channel.sudo().channel_fetch_message(last_id, limit)